Arrangement for shielding amplifiers



Au 22, 1939; .v. GANDTNER ARRANGEMENT FOR SHIELDING AMPLIFIERS FiledMarch 9, 1937 j K v 7 .g 4 H 5' nli lnlrl L59 'Ba INVENTOR.

BY I

} ATTORNEY;

Patented Aug. 22, 1939 UNITED STATES PATENT OFFICE ARRANGEMENT FORSHIELDING AMPLIFIERS Application March 9, 1937, Serial No. 129,823

In Germany March 9, 1936.

5 Claims.

connected with one another and with a point of the amplifier connectionare to keep away also external disturbances. Furthermore, it is alsoknown to ground the shields.

It has, however, been found that this simple shielding is not alwayssufiioient to prevent regenerative phenomena and to keep away externaldisturbances, since it has been ascertained that in shielded amplifiers,particularly in amplifiers in high-frequency transmission systems,notwithstanding the usual shielding, external disturbances weretransmitted to the grid circuit and regenerative phenomena occurred.These phenomena are, among other things, due to the fact that potentialdifferences are set up between the input and output circuit of theamplifier thus causing interfering currents.

. To avoid these drawbacks the amplifiers, particularly thehigh-frequency amplifiers for wide.

V band systems, are surrounded according to the invention by twotelescopically arranged metallic shields, the inner shield beingconnected to a point of the amplifier connection, preferably to thecathode. In the inner metallic shield, metallic partition walls may beprovided in a manner well known which protect the amplifier inputagainst the amplifier output. When using various amplifier steps, suchpartition walls are preferably provided between each step.

The voltage sources necessary for the grid,

filament, and anode voltages are preferably armission, which isinsulatedly surrounded by a metallic covering, for instance, by a leadsheath, the inner shield of the amplifier is connected according to theinvention to the return conductor and the outer shield to the metalliccovering of the double conducton In this case, the shields are sodesigned and so connected to the return conductor and to the lead sheathas to be completely shielded, that is to say, the inner shieldconstitutes a continuation of the return conductor and the outer shielda continuation of the lead sheath; for instance, the shields areprovided with branches which may be arranged on the return conductor andthe lead sheath respectively or placed thereon by slidable sleeves. Inthe case of transmission systems with various coaxial double conductorsand a common metallic sheath, the inner shields of the amplifiers areconnected with the corresponding return conductors and a common outershield is connected to the sheath.

Coaxial conductor arrangements are employed to advantage for the highfrequency transmission of very wide frequency bands, particularly oftelevision currents. They are non-symmetric with respect to ground. Itis, therefore, necessary to determine exactly the potential of theindividual conductors in order that, for instance, no loops are formedby multiple grounding. This is particularly important at the point atwhich amplifiers are inserted, since back couplings may easily occurwithin the amplifiers by the formation of such loops. In general, thecapacity of the return conductor with respect to the metallic sheathinsulatedly arranged thereon and in the case of underground cablesdirectly connected to ground or the capacity of the inner shield of theamplifier with respect to the outer shield, suffices to determineexactly the potential of the return conductor. Owing to the influence byheavy currents it is, however, possible that a charge occurs between thereturn conductor and the sheath. In such cases, the inner shield of theamplifier is preferably metallically connected to the outer shield.However, it is essential that this connection take place at a singlepoint in order to avoid earth circuits. In the case of various shieldedspaced amplifier arrangements in such a high-frequency transmissionsystem, it is preferable to connect only the inner shield of anamplifier arrangement to the corresponding outer shield at one point.Instead of a galvanic, a capacitive connection may under circumstancesbe sufficient.

The invention may also be used in amplifiers which are arranged in highfrequency transmission systems with symmetrical double conductors.Although symmetrical conductors, owing to their symmetry with respect toearth, are considerably more insensitive to external disturbances thancoaxial conductors, the same conditions prevail at the points in whichamplifiers are inserted as is the case with coaxial conductors. Inamplifiers in a high frequency transmission system with shieldedsymmetrical double conductors the inner shield of the amplifier isconnected according to the invention to a point of the amplifierconnection and the outer shield to the metallic sheath.

For a better understanding of the nature of my invention reference maybe had to the following description taken in connection with theaccompanying drawing, in which Fig. 1 shows the use of the invention fortransmission systems with coaxial conductora and Fig. 2 for transmissionsystems with symmetrical conductors.

In Fig. 1, L denotes the internal conductor of an air-insulated coaxialdouble conductor. Around the inner conductor is arranged a spacing piecenot. shown, for instance, a styrofiex spiral. Pairs, quads or the likenot shown employed, for the low frequency transmission of intelligencemay be placed on the return conductor RL. On an insulation layer is thenplaced a metallic shield M, for instance, the lead sheath of the cablewhich may be provided in the usual manner with a wire armoring and ajute covering.

The return conductor BL is enlarged to a closed space S1 in such amanner as to receive all elements of the amplifier. The enlargement ofthe return conductor is effected by a metallic shield S1 which isintimately connected to the return conductors RL at both sides by branchsleeves placed over the return conductors. Inside the shield S1 arearranged the amplifier elements in such a manner that the cathode K ofthe amplifier tube V is connected to the return conductor RL and to theshield S1 respectively. The internal conductor L is connected to theshield through the primary winding of the repeater VU. Undercircumstances, adaptation elements may further be arranged in serieswith the primary winding. The secondary winding of the repeater VU isconnected to the grid of the amplifier tube V whose anode circuit isconnected to the coaxial conductor L, RL through the repeater NU. Theamplifier inlet and outlet are separated by a metallic partition wall T.The shield is provided with bushings for the supply of the grid,filament, and anode voltages. In the grid and anode cir cuit arepreferably arranged filtering means Gly and Grid connected to thecathode through capacitors Cg and Ca. The shield S1 and the currentsupply circuit is properly insulated against ground.

Also the shield M- is enlarged to a metallic shield S11 which may alsobe placed on the shields M by means of branch sleeves. The shield S1 maybe connected in a point E to the shield S11 galvanically orcapacitively. The shield S11 is preferably also insulated against groundand is only connected at the joints to the shield M and, therefore. toearth. The shield S11 may, for instance, be obtained by covering theentire amplifier space with thin sheet copper or with a wire gauze. Thepower sources Bg and Ba for the grid and anode voltage are arrangedexternally of the shield S11. In order to keep away high frequencyinterfering voltages from the inside of the shielded space, it isnecessary to choke the supply leads immediately before the introduction(Dru, and Dry) and to cause the interfering voltages to act on theshield S11. The filament voltage source is not shown.

The shielded amplifier arrangement for transmission systems withsymmetrical double conductors is denoted in Fig. 2 by the samecharacters of reference as in Fig. 1. The voltage sources are not shownin order not to complicate the drawing. L denotes both symmetricalconductors, M the shielding of the symmetrical conductors. The innershield S1 is connected to a point of the amplifier connection,preferably to the cathode. The connection of the shield S1 with thereturn conductor is omitted in this arrangement. However, also in thiscase a charge of the shield S1 with respect to the shield S11 may occurby the effect of a heavy current. Also in this case the inner shield maypreferably be connected to the outer shield galvanically orcapacitively.

I claim as my invention:

1.. In combination, an electron discharge device amplifier having acathode, anode, and control electrode; an input circuit connectedbetween said control electrode and cathode; an output circuit connectedbetween said anode and cathode; a first metallic shielding containersurrounding said amplifier, its input and output circuits; a secondmetallic shielding container surrounding and spaced from said firstcontainer; a metallic partition wall in said first container separatingsaid first container into two chambers, said input circuit being in onechamber, and said output circuit being in the other chamber; a path oflow impedance to radio frequency energy connected between said cathodeand said first container, and means coupling one point on said firstshielding container to a point on said second shielding container.

2. In combination, an electron discharge device amplifier having acathode, anode, and control electrode; an input circuit connectedbetween said control electrode and cathode; an output circuit connectedbetween said anode and cathode; a first metallic shielding containersurrounding said amplifier, its input and output circuits; a secondmetallic shielding container surrounding and spaced from said firstcontainer; a metallic partition wall in said first container separatingsaid first container into two chambers, said input circuit being in onechamber, and said output circuit being in the other chamber; a path oflow impedance to radio frequency energy connected between said cathodeand said first container; a first coaxial cable having its innerconductor in one chamber coupled to said control electrode and its outerconductor connected to said first container; and a second coaxial cablehaving its inner conductor in the other chamber coupled to said anode,and its outer conductor also coupled to said first container.

3. In combination, an electron discharge device amplifier having acathode, anode, and control electrode; an input circuit connectedbetween said control electrode and cathode; an output circuit connectedbetween said anode and cathode; a first metallic shielding containersurrounding said amplifier, its input and output circuits; a secondmetallic shielding container surrounding and spaced from said firstcontainer; a metallic partition Wall in said first container separatingsaid first container into two chambers, said input circuit being in onechamher, and said output circuit being in the other chamber; a path oflow impedance to radio frequency energy connected between said cathodeand said first container; a first coaxial cable having its innerconductor in one chamber coupled to said control electrode and its outerconductor connected to said first container; a sec ond coaxial cablehaving its inner conductor in the other chamber coupled to said anode,and its outer conductor also coupled to said first container; and ametallic sheath insulated from and surrounding each of said coaxialcables, said sheaths both being connected to said second metalliccontainer.

4. In combination, an electron discharge device amplifier having acathode, anode, and control electrode; an input circuit connectedbetween said control electrode and cathode; an output circuit connectedbetween said anode and cathode; a first metallic shielding container surrounding said amplifier, its input and output circuits; a secondmetallic shielding container surrounding and spaced from said firstcontainer; a metallic partition wall in said first container separatingsaid first container into two chambers, said input circuit being in onechamber, and said output circuit being in the other chamber; a path oflow impedance to radio frequency energy connected between said cathodeand said first container; a source of energy comprising a pair of leadscoupled to said input circuit; and a utilization circuit comprisinganother pair of leads coupled to said output circuit, a metallic sheathinsulated from and surrounding each of said pairs of leads, said sheathsbeing connected to said second metallic container.

5. A system in accordance with claim 4, including a direct connectionfrom solely one point on said first shielding container to a point onsaid second shielding container.

VALENTIN GANDTNER.

